Scroll compressor

ABSTRACT

The present disclosure relates to a scroll compressor. According to the present disclosure, an oldham ring for preventing the rotation movement of a orbiting scroll may be fabricated by sintering metal powder to have a yield stress above 300 MPa, and thus even when a gas force is eccentrically generated it may be possible to prevent the oldham ring supporting the circular movement of the orbiting scroll from being damaged due to this, thereby enhancing the compressor performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority Korean Application No. 10-2011-0098598, filed in Korea on Sep. 28, 2011, which is herein expressly incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

A scroll compressor is disclosed herein.

2. Description of the Related Art

Scroll compressor may include a fixed scroll having a fixed wrap and a orbiting scroll having a orbiting wrap. The scroll compressor provides a method of inhaling and compressing refrigerant through a continuous volume change of the compression chamber formed between the fixed wrap and the orbiting wrap while the orbiting scroll performs a circulating movement on the fixed scroll.

Furthermore, the scroll compressor continuously performs inhalation, compression and discharge, and thus has excellent characteristics in the aspect of vibration and noise generated during its operational process compared to other types of compressors.

In a scroll compressor, the behavior characteristic is determined by its type of the fixed wrap and orbiting wrap. The fixed wrap and orbiting wrap may have an arbitrary shape, but typically have an involute curved shape that can be easily processed. The involute curve denotes a curve corresponding to a trajectory drawn by a cross section of thread when unloosing thread wound around a base circle having an arbitrary radius. When using such an involute curve, the capacity change rate is constant because a thickness of the wrap is constant and thus the number of turns should be increased to obtain a sufficient level of compression ratio, but it may also increase the size of the compressor.

On the other hand, the orbiting scroll is typically formed with a disk shaped end plate and the orbiting wrap at the side of the end plate. Furthermore, a boss portion is formed at a rear surface on which the orbiting wrap is not formed and connected to a rotation shaft for circulating the orbiting scroll. Such a shape may form a orbiting wrap over a substantially overall area of the end plate, thereby decreasing a diameter of the end plate portion for obtaining the same compression ratio. However, on the contrary, the operating point to which a repulsive force of refrigerant is applied and the operating point to which a reaction force for cancelling out the repulsive force is applied are separated from each other in an axial direction, thereby causing a problem of increasing vibration or noise while the orbiting scroll is tilted during the operational process.

As a method for solving such problems, there has been disclosed a so-called shaft penetration scroll compressor which is a type that a position at which the rotation shaft and the orbiting scroll are combined with each other is formed on the same surface as the orbiting wrap. In such a type of compressor, the operating point of a repulsive force and the operating point of the reaction force are applied at the same position, thereby solving a problem that the orbiting scroll is inclined.

In a shaft penetration scroll compressor in the related art as described above, a ring shaped oldham ring (Oldham's ring) 3 is provided between the orbiting scroll 1 and the fixed scroll 4 to prevent the rotation movement of the orbiting scroll 1.

The oldham ring 3, as illustrated in FIG. 2, may be formed of a ring portion 31 having a substantially circular shape inserted into a rear surface of the end plate portion of the orbiting scroll 1 and a pair of a first key 32 and a second key 33 protruded to both upper and lower lateral surfaces of the ring portion 31, respectively, or protruded to one lateral surface thereof (an example of being protruded to one lateral surface in the drawing). The first key 32 and second key 33 are alternately formed at 90 degrees intervals along a circumferential direction of the ring portion 31 to be crossed perpendicular to each other.

Furthermore, the first key 32 may be formed to be protruded longer than the thickness of an outer circumferential side of the end plate portion of the orbiting scroll 1 in the direction of facing the fixed scroll at an outer circumferential surface of the ring portion 31, and the second key 33 may be formed to be protruded shorter than the first key 32 in the direction of facing the orbiting scroll 1 at an outer circumferential surface of the ring portion 31. The first key 32 should be combined with the fixed scroll 4 by interposing the orbiting scroll 1 and thus formed to be bent at a predetermined distance from an outer circumferential surface of the ring portion 31, but the second key 33 is combined with the orbiting scroll 1 combined with the ring portion 31 of the oldham ring and thus formed to be continuously protruded from an outer circumferential surface of the ring portion 31 to a bottom surface thereof.

The first key 32 is inserted into an inner portion of the first key groove (not shown) formed from an upper end of the side wall portion of the fixed scroll 4 to an upper surface of the support portion supporting the orbiting scroll, and the second key 33 is combined with the second key groove 11 formed at an outer circumferential portion of the end plate portion of the orbiting scroll 1.

However, the foregoing oldham ring in the related art is formed such that the keys 31, 32 of the oldham ring 3 can be slid in the direction substantially perpendicular to the rotational direction of the orbiting scroll 1 to suppress the rotation movement of the orbiting scroll 1, and thus the keys 32, 33 of the oldham ring 3 receive a large stress load. Moreover, in a shaft penetration scroll compressor, the discharge port is eccentrically formed with respect to the axial center thereof and thus a gas force is eccentrically generated and due to this the z-directional moment of the keys 31, 32 of the oldham ring 3 is increased to receive a larger stress load, and as a result there has been a problem of causing the damage of the oldham ring fabricated by casting.

SUMMARY OF THE INVENTION

An object of the present disclosure is to provide a scroll compressor capable of preventing an oldham ring from being damaged by a load in advance.

In order to accomplish the foregoing object, there is provided a scroll compressor, including a fixed scroll having a fixed wrap; a orbiting scroll configured to have a orbiting wrap engaged with the fixed wrap to form a first and a second compression chamber at an inner surface and an outer surface thereof, and perform a orbiting with respect to the fixed scroll; a frame provided at an opposite side of the fixed scroll by interposing the orbiting scroll to support the orbiting scroll; a rotation shaft configured to have an eccentric portion at an end portion thereof, and combined with the orbiting scroll such that the eccentric portion is overlapped with the orbiting wrap in a radial direction; a driving unit configured to drive the rotation shaft; and a rotation prevention member configured to prevent the rotation of the orbiting scroll, wherein the rotation prevention member is formed to have a yield stress above 300 MPa.

In order to accomplish the foregoing object, there is provided a scroll compressor, including a fixed scroll having a fixed wrap to be protruded at a lateral surface of a end plate portion; a orbiting scroll configured to have a orbiting wrap engaged with the fixed wrap to form a first and a second compression chamber at an inner surface and an outer surface thereof at a lateral surface of the end plate portion, and perform a orbiting with respect to the fixed scroll; a frame provided at an opposite side of the fixed scroll by interposing the orbiting scroll to support the orbiting scroll; a rotation shaft configured to have an eccentric portion at an end portion thereof, and combined with the orbiting scroll such that the eccentric portion is overlapped with the orbiting wrap in a radial direction; a driving unit configured to drive the rotation shaft; and a rotation prevention member configured to prevent the rotation of the orbiting scroll, wherein the rotation prevention member includes a ring portion inserted into a rear surface of the end plate portion of the orbiting scroll; a first key protruded from a lateral surface of the ring portion to be inserted into the fixed scroll; and a second key protruded from a lateral surface of the ring portion at a predetermined distance from the first key to be inserted into the orbiting scroll.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

In the drawings:

FIG. 1 is a cross-sectional view illustrating a compression unit in a shaft penetration scroll compressor in the related art;

FIG. 2 is a plan view illustrating an oldham ring in a compression unit according to FIG. 1;

FIG. 3 is a cross-sectional view schematically illustrating a scroll compressor according to an embodiment of the present disclosure;

FIG. 4 is a partial cross-sectional view illustrating a compression unit in the embodiment illustrated in FIG. 3;

FIG. 5 is an exploded perspective view illustrating a compression unit illustrated in FIG. 4;

FIGS. 6A and 6B are a plan view illustrating a first and a second compression chamber immediately subsequent to inhalation and immediately prior to discharge in a scroll compressor having a orbiting wrap and a fixed wrap with an involute shape;

FIGS. 7A and 7B are a plan view illustrating a type of orbiting wrap in a scroll compressor having a orbiting wrap and a fixed wrap with another involute shape;

FIG. 8 is a plan view illustrating a orbiting wrap and a fixed wrap obtained by another envelope line;

FIG. 9 is an enlarged plan view illustrating a central portion thereof in FIG. 8;

FIG. 10 is a plan view illustrating a configuration in which the orbiting wrap is located prior to 150° starting discharge in the embodiment illustrated in FIG. 8;

FIG. 11 is a plan view illustrating a time point at which discharge is started from the second compression chamber in the embodiment illustrated in FIG. 8; and

FIG. 12 is a graph for explaining technical background requiring an oldham ring according to the present embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a scroll compressor according to the present disclosure will be described in detail based on an embodiment illustrated in the accompanying drawings.

Referring to FIG. 3, a scroll compressor according to the present embodiment has a cylindrically shaped casing 110, and an upper shell 112 and a lower shell 114 for covering an upper portion and a lower portion of the casing, respectively. The upper shell and lower shell may be bonded to the casing to form one confined space together with the casing.

A discharge pipe 116 may be provided at an upper portion of the upper shell 112. The discharge pipe 116 corresponds to a path through which compressed refrigerant is discharged to the outside, and an oil separator (not shown) for separating oil mixed with the discharged refrigerant may be connected to the discharge pipe 116. Furthermore, a suction pipe 118 is provided at a lateral surface of the casing 110. As a path through which refrigerant to be compressed flows, the suction pipe 118 is located at a boundary surface between the casing 110 and the upper shell 112 in FIG. 3, but the location may be set at discretion. Moreover, the lower shell 114 may also function as an oil chamber for storing oil supplied to operate the compressor in an efficient manner.

A motor 120 as a driving unit may be provided at a substantially central portion of the inner portion of the casing 110. The motor 120 may include a stator 122 fixed to an inner surface of the casing 110 and a rotor 124 located at an inner portion of the stator 122 to be rotated by an interaction with the stator 122. A rotation shaft 126 is combined with the center of the rotor 124 and rotated together with the rotor 124.

An oil passage 126 a may be formed at an central portion of the rotation shaft 126 to be extended along a length direction of the rotation shaft 126, and an oil pump 126 b for supplying oil stored in the lower shell 114 to the upper portion thereof may be provided at a lower end portion of the rotation shaft 126. The oil pump 126 b may have a shape in which a spiral groove is formed or a separate impeller is provided at an inner portion of the oil passage, and a separate capacity type pump may be provided therein.

An enlarged diameter portion 126 c inserted into an inner portion of the boss portion formed on the fixed scroll which will be described later may be formed at an upper end portion of the rotation shaft 126. The enlarged diameter portion may be formed to have a diameter larger than the other portion thereof, and a pin portion 126 d forming an eccentric portion together with the eccentric bearing 128 which will be described later may be formed at an end portion of the enlarged diameter portion. The eccentric bearing 128 for forming an eccentric portion together with the pin portion 126 d may be inserted into the pin portion 126 d, and referring to FIG. 5, the eccentric bearing 128 may be eccentrically inserted with respect to the pin portion 126 d, and a combining portion for both may be asymmetrically formed in a substantially “D” shape based on the center of the pin portion such that the eccentric bearing 128 is not rotated with respect to the pin portion 126 d.

A fixed scroll 130 may be mounted on a boundary portion between the casing 110 and upper shell 112. The fixed scroll 130 may be pushed and fixed between the casing 110 and the upper shell 112 in a shrink fit manner or combined together with the casing 110 and upper shell 112 by welding.

A boss portion 132 into which the foregoing rotation shaft 126 is inserted may be formed at a bottom surface of the fixed scroll 130. A penetration hole through which the pin portion 126 d of the rotation shaft 126 passes may be formed at an upper side surface (based on FIG. 3) of the boss portion 132 and thus the pin portion 126 d may be protruded in the upward direction of the end plate portion 134 of the fixed scroll 130 therethrough.

A fixed wrap 136 engaged with the orbiting wrap which will be described later to form a compression chamber may be formed at an upper portion surface of the end plate portion 134, and a space portion for accommodating the orbiting scroll 140 which will be described later may be formed, and a lateral wall portion 138 adjoining an inner circumferential surface of the casing 110 may be formed at an outer circumferential portion of the end plate portion 134. A orbiting scroll support portion 138 a on which an outer circumferential portion of the orbiting scroll 140 is placed may be formed at an inner side of the upper end portion of the lateral wall portion 138, and the height of the orbiting scroll support portion 138 a may be formed to have the same height as the fixed wrap 136 or to have a height slightly less than that of the fixed wrap, and thus an end portion of the orbiting wrap can be brought into contact with a surface of the end plate portion of the fixed scroll.

The orbiting scroll 140 may be provided at an upper portion of the fixed scroll 130. The orbiting scroll 140 may be formed with a substantially circular shaped end plate portion 142 and a orbiting wrap 144 engaged with the fixed wrap 136. A substantially circular shaped rotation shaft combining portion 146 rotatably inserted and fixed to the eccentric bearing 128 may be formed at a central portion of the end plate portion 142. An outer circumferential portion of the rotation shaft to combining portion 146 may be connected to the orbiting wrap to perform the role of forming a compression chamber together with the fixed wrap during the compression process. It will be described later.

On the other hand, the eccentric bearing 128 may be inserted into the rotation shaft combining portion 146 and thus an end portion of the rotation shaft 126 may be inserted through the end plate portion of the fixed scroll, and the orbiting wrap, fixed wrap and eccentric bearing 128 may be provided to be overlapped with one another in the radial direction of the compressor. During compression, a repulsive force of refrigerant may be applied to the fixed wrap and orbiting wrap, and a compression force may be applied between the rotation shaft support portion and eccentric bearing as a reaction force thereto. As described above, when part of the shaft is overlapped with the wrap in a radial direction through the end plate portion, the repulsive force and compression force of refrigerant may be applied to the same surface based on the end plate, and thus they may be cancelled out by each other. Due to this, it may be possible to prevent the inclination of the orbiting scroll by the operation of the compression force and repulsive force.

Furthermore, though not shown in the drawing, a discharge hole may be formed on the end plate portion 142 and thus compressed refrigerant may be discharged to an inner portion of the casing. The location of the discharge hole may be set at discretion by taking a required discharge pressure or the like into consideration.

On the other hand, an upper frame 170 is provided at an upper portion of the orbiting scroll 140, and a hole communicated with a discharge hole of the orbiting scroll 140 to discharge compressed refrigerant to the side of the upper shell is formed at the center of the upper frame 170.

Furthermore, a lower frame 160 for rotatably supporting a lower side of the rotation shaft 126 is provided at a lower portion of the casing 110.

FIGS. 6A and 6B are a plan view illustrating a compression chamber immediately subsequent to inhalation and a compression chamber immediately prior to discharge in a scroll compressor having a orbiting wrap and a fixed wrap formed with an involute curve, and having a configuration that part of the shaft penetrates the end plate. FIG. 6A is a view illustrating a change of the first compression chamber formed between an inner lateral surface of the fixed wrap and an outer lateral surface of the orbiting wrap, and FIG. 6B is a view illustrating a change of the second compression chamber formed between an inner lateral surface of the orbiting wrap and an outer lateral surface of the fixed wrap.

In the scroll compressor, the compression chamber may be created between two contact points generated when the fixed wrap and orbiting wrap are brought into contact with each other, and in case of the fixed wrap and orbiting wrap with an involute curve, two contact points defining one compression chamber as illustrated in FIG. 4 may be located on a straight line. In other words, the compression chamber may be disposed over 360° with respect to the center of the rotation shaft.

Considering a volume change of the first compression chamber in FIG. 6A, the volume of the compression chamber immediately subsequent to inhalation located at the outside may be gradually reduced while moving to the central portion thereof by a circular movement of the orbiting scroll, and thus has a minimum value when reaching an outer circumferential portion of the rotation shaft combining portion located at the center of the orbiting scroll. In case of the fixed wrap and orbiting wrap with an involute curve, the volume reduction rate may be linearly reduced as increasing the rotation angle of the rotation shaft, and thus the compression chamber should be moved closely to the center if possible, to obtain a high compression ratio, but in case where the rotation shaft exists at the center as described above, it can be moved only to an outer circumferential portion of the rotation shaft. Due to this, the compression ratio may be reduced, and the compression ratio is about 2.13 in FIG. 6A.

On the other hand, the second compression chamber illustrated in FIG. 6B may have a lower compression ratio compared to the first compression chamber, and thus have a value of about 1.46. However, in case of the second compression chamber, when a connecting portion between the rotation shaft combining portion (P) and the orbiting wrap is formed with a circular arc shape as illustrated in FIG. 7A, a compression path of the second compression chamber may be lengthened, thereby increasing the compression ratio up to a level of 3.0. In this case, the second compression chamber may have a range of less than 360 degrees immediately prior to discharge. However, such a method cannot be applicable to the first compression chamber.

Accordingly, in case of the fixed wrap and orbiting wrap with an involute shape, an intentional level of compression ratio can be obtained in case of the second compression chamber, but it may be impossible in case of the first compression chamber, and as a result, in case that there is a remarkable difference of compression ratio between the two compression chambers, it will affect a bad effect on the operation of the compressor.

In order to solve the foregoing problem, the fixed wrap and orbiting wrap may be formed to have another curve other than the involute curve. Referring to FIGS. 8 and 9, when the center of the rotation shaft combining portion 146 is “O”, and two contact points are “P1, P2”, respectively, it is seen that an angle α defined by two straight lines connecting the two contact points (P1, P2) to the center (O) of the rotation shaft combining portion is less than 360°, and also a distance “I” between perpendicular vectors at each contact point has a value greater than “0”. Due to this, the first compression chamber immediately prior to discharge may have a volume less than a case of the fixed wrap and orbiting wrap formed with an involute curve, thereby increasing the compression ratio. Furthermore, the orbiting wrap and fixed wrap illustrated in FIG. 8 may have a configuration in which the diameter and starting point thereof are connected to a plurality of different circular arcs, and the outermost curve may have a substantially oval shape having the major and minor axes.

Furthermore, a protrusion portion 137 protruded to the side of the rotation shaft combining portion 146 may be formed adjacent to an inner side end portion of the fixed wrap, and a contact portion 137 a formed to be protruded from the protrusion portion may be additionally formed on the protrusion portion 137. In other words, the inner side end portion of the fixed wrap may be formed to have a thickness greater than the other portion thereof. Due to this, a strength of the inner side end portion of the wrap receiving the highest compression force on the fixed wrap can be enhanced, thereby enhancing the durability.

On the other hand, the thickness of the fixed wrap is gradually decreased from the contact point (P1) located at an inner side between the two contact points forming the first compression chamber at a discharge start time point as illustrated in FIG. 9 in the contact portion 137 a. Specifically, a first decreasing portion 137 b adjacent to the contact point (P1) and a second decreasing portion 137 c adjacent to the first decreasing portion are formed, and a thickness reduction rate at the first decreasing portion may be greater than that at the second decreasing portion. Furthermore, the thickness of the fixed wrap may be increased for a predetermined section subsequent to the second decreasing portion.

Furthermore, when a distance between an inner surface of the fixed wrap and the axial center (O′) of the rotation shaft is DF, the DF may be decreased after being increased as moving in a counter clockwise direction (based on FIG. 9) from the P1, and the section thereof is shown in FIG. 10. FIG. 10 is a plan view illustrating the location of the orbiting wrap prior to 150° starting discharge, and the orbiting wrap may reach a configuration illustrated in FIG. 8 when the rotation shaft is further rotated by 150° from the configuration of FIG. 10. Referring to FIG. 10, the contact point is located at an upper side of the rotation shaft combining portion 146, and the DF may be increased and then decreased during the section between P1 of FIG. 8 and P1 of FIG. 10.

A concave portion 145 engaged with the protrusion portion may be formed at the rotation shaft combining portion 146. A lateral surface of the concave portion 145 may be brought into contact with the contact portion 137 a of the protrusion portion 137 to form a side contact point of the first compression chamber. When a distance between the center of the rotation shaft combining portion 146 and an outer circumferential portion of the rotation shaft combining portion 146 is “Do”, the “Do” may be increased and then decreased during the section between P1 of FIG. 8 and P1 of FIG. 10. Similarly, the thickness of the rotation shaft combining portion 146 may be also increased and then decreased during the section between P1 of FIG. 8 and P1 of FIG. 10.

Furthermore, a side wall of the concave portion 145 may include a first increasing portion 145 a in which the thickness thereof is drastically increased in a relatively high rate and a second increasing portion 145 b connected to the first increasing portion in which the thickness is increased in a relatively low rate. They may correspond to the first decreasing portion and the second decreasing portion, respectively. The first increasing portion, first decreasing portion, second increasing portion, and second decreasing portion are obtained as a result of bending the envelope line toward the rotation shaft combining portion. Due to them, an inner side contact point (P1) forming the first compression chamber may be located at the first increasing portion and second increasing portion, and as a result, the compression ratio can be increased by decreasing the length of the first compression chamber immediately prior to discharge.

The other side wall of the concave portion 145 may be formed to have a circular arc shape. The diameter of the circular arc may be determined by a wrap thickness of the end portion of the fixed wrap and a circular radius of the orbiting wrap, and the diameter of the circular arc may be increased as increasing the thickness of the end portion of the fixed wrap. Due to this, the thickness of the orbiting wrap around the circular arc may be also increased to secure the durability, and the compression path may be lengthened and thus have an advantage of increasing the compression ratio of the second compression chamber as much as the lengthened path.

Here, a central portion of the concave portion 145 may form part of the second compression chamber. FIG. 11 is a plan view illustrating the location of the orbiting wrap when discharge is started from the second compression chamber, and the second compression chamber is located adjacent to a circular shaped side wall of the concave portion in FIG. 11, and when the rotation shaft is further rotated, an end portion of the second compression chamber may pass through a central portion of the concave portion.

On the other hand, an oldham ring 150 for preventing the rotation of the orbiting scroll may be provided at an upper side of the orbiting scroll 140.

The oldham ring 150, as illustrated in FIGS. 4 and 5, may be formed of a ring portion 152 having a substantially circular shape inserted into a rear surface of the end plate portion 142 of the orbiting scroll 140 and a pair of a first key 154 and a second key 156 protruded to both upper and lower lateral surfaces of the ring portion 152, respectively, or protruded to one lateral surface thereof (an example of being protruded to one lateral surface in the drawing). The first key 154 and second key 156 are alternately formed at 90 degrees intervals along a circumferential direction of the ring portion 152 to be crossed perpendicular to each other.

Furthermore, the first key 154 may be formed to be protruded longer than the thickness of an outer circumferential side of the end plate portion 142 of the orbiting scroll 140 in the direction of facing the fixed scroll 130 at an outer circumferential surface of the ring portion 152, and the second key 156 may be formed to be protruded shorter than the first key 154 in the direction of facing the orbiting scroll 140 at an outer circumferential surface of the ring portion 152. The first key 154 should be combined with the fixed scroll 130 by interposing the orbiting scroll 140 and thus formed to be bent at a predetermined distance from an outer circumferential surface of the ring portion 152, but the second key 156 is combined with the orbiting scroll 140 combined with the ring portion 152 of the oldham ring and thus formed to be continuously protruded from an outer circumferential surface of the ring portion 152 to a bottom surface thereof.

The first key 154 is inserted into an inner portion of the first key groove 154 a formed from an upper end of the side wall portion 138 of the fixed scroll 130 to an upper surface of the support portion 138 a supporting the orbiting scroll 140, and the second key 156 is combined with the second key groove 156 a formed at an outer circumferential portion of the end plate portion 142 of the orbiting scroll 140.

Here, the first key groove 154 a may be formed to have a vertical portion extended in the upward direction and a horizontal portion extended in the left/right direction, and a lower side end portion of the first key 154 may always maintain a state of being inserted in the horizontal portion of the first key groove 154 a, but an outer side end portion of the first key 154 in the radial direction may be formed to be released from the vertical portion of the first key groove 154 a during the circular movement of the orbiting scroll. In other words, a coupling between the first key groove 154 a and the fixed scroll may be made in the vertical direction, thereby reducing the diameter of the fixed scroll.

Specifically, a clearance as much as corresponding to a circular radius should be secured between an end plate of the orbiting scroll and an inner wall of the fixed scroll. If a key of the oldham ring is combined with the fixed scroll in the radial direction, then the length of a key groove formed on the fixed scroll should be at least greater than the circular radius to prevent the oldham ring from being released from the key groove during the circular process, and it may be a cause of increasing the size of the fixed scroll.

On the contrary, as in the above embodiment, if the key groove is extended to a lower space between the end plate and the orbiting wrap in the orbiting scroll, it may be possible to secure a sufficient length of the key groove and reducing the size of the fixed scroll.

Moreover, in the above embodiment, all keys are formed at a lateral surface of the ring portion, and thus the height of the compression unit in the axial direction can be reduced compared to a case that keys are formed, respectively, in both lateral surfaces thereof.

On the other hand, it may be required that the strength of the foregoing oldham ring is varied according to the shape of the shaft penetration scroll compressor. In other words, during a typical involute compression in which the wrap is formed in an involute curve, the discharge port is formed in a substantially concentric manner with respect to the axial center of the rotation shaft, and thus the z-directional moment is not increased to a large extent. However, in case of an involute circular arc compression, the discharge port is eccentrically moved from the axial center of the rotation shaft by a predetermined level and thus the z-directional moment is increased, and as a result, a load being transferred to the oldham ring may be increased compared to a typical involute compression type scroll compressor other than a shaft penetration scroll compressor. Accordingly, in a shaft penetration scroll compressor including an involute circular arc compression, the strength of the oldham ring should be increased to prevent the oldham ring from being damaged.

In particular, during a so-called crescendo type circular arc compression in which the protrusion portion is formed at a starting end of the wrap as in the present embodiment, the discharge port is located in a more eccentric manner, thereby further increasing the z-directional moment. Accordingly, a load being transferred to the oldham ring may be increased to such an extent. Moreover, when the first key and second key are formed to be protruded at a lateral surface of the ring portion, the length of the first key may be increased and thus a load being transferred to the first key may be increased to a large extent compared to the strength of the first key. FIG. 12 is a graph illustrating a maximum load with respect to a typical involute compression, an involute circular arc compression, and a crescendo circular arc compression, respectively.

As illustrated in the drawing, it is seen that the maximum load at the oldham ring in a scroll compressor is approximately 54 N in case of a typical involute compression with 5.5 horse power and approximately 140 N in case of an involute circular arc compression. On the contrary, in case of a crescendo circular arc compression as in the present embodiment, the eccentric level of the discharge port is further increased compared to the involute circular arc compression, and thus the maximum load of about 230 N can be transferred to the oldham ring. The maximum load may be increased by about four times compared to the involute compression or about 40% compared to the involute circular arc compression. Accordingly, the oldham ring fabricated by the existing casting method may be fractured without withstanding the maximum load during a so-called crescendo shaped circular arc compression.

Typically, the oldham ring with a casting method may be subject to a Fujimite surface treatment with aluminium (ALDC 8) to provide a yield stress of approximately 282 MPa. In case of the involute compression or involute circular arc compression, the oldham ring can withstand the maximum load which is 54 N and 140 N, respectively. However, in case of the crescendo circular arc compression, the oldham ring with a casting method cannot withstand the maximum load which is about 230 N.

Accordingly, according to the present embodiment, the oldham ring is to fabricated through a sintering process to increase a yield stress of the oldham ring to above approximately 300 N. The oldham ring may be fabricated by sintering stainless steel powder. The fundamental configuration and operation of the oldham ring are the same as those of the foregoing example and thus the description thereof will be omitted.

As a result, the strength of the oldham ring may be enhanced to a large extent, and thus it may be possible to prevent the oldham ring from being damaged even in case of the crescendo circular arc compression in which the maximum load to the oldham ring is increased, thereby enhancing the compression reliability. 

What is claimed is:
 1. A scroll compressor, comprising: a fixed scroll having a fixed wrap; a orbiting scroll configured to have a orbiting wrap engaged with the fixed wrap to form a first and a second compression chamber at an inner surface and an outer surface thereof, and perform a orbiting with respect to the fixed scroll; a frame provided at an opposite side of the fixed scroll by interposing the orbiting scroll to support the orbiting scroll; a rotation shaft configured to have an eccentric portion at an end portion thereof, and combined with the orbiting scroll such that the eccentric portion is overlapped with the orbiting wrap in a radial direction; a driving unit configured to drive the rotation shaft; and a rotation prevention member configured to prevent the rotation of the orbiting scroll, wherein the rotation prevention member is formed to have a yield stress above 300 MPa.
 2. The scroll compressor of claim 1, wherein when the rotation prevention member is formed by sintering stainless steel powder.
 3. The scroll compressor of claim 1, wherein the first compression chamber is formed between two contact points (P1, P2) generated when an inner surface of the fixed wrap and an outer surface of the orbiting wrap are brought into contact with each other, and when an angle having a greater value between angles made by two lines connecting the center (O) of the eccentric portion to the two contact points (P1, P2), respectively, is α, α<360° at least prior to starting discharge.
 4. The scroll compressor of claim 3, wherein when a distance between perpendiculars at the two contact points (P1, P2) is I, I>0.
 5. The scroll compressor of claim 1, wherein a rotation shaft combining portion combined with the eccentric portion at an inner portion thereof is formed at a central portion of the orbiting scroll, and a protrusion portion is formed at an inner circumferential surface of an inner end portion of the fixed wrap, and a concave portion brought into contact with the protrusion portion to form a compression chamber is formed at an outer circumferential surface of the rear surface combining portion.
 6. A scroll compressor, comprising: a fixed scroll having a fixed wrap to be protruded at a lateral surface of a end plate portion; a orbiting scroll configured to have a orbiting wrap engaged with the fixed wrap to form a first and a second compression chamber at an inner surface and an outer surface thereof at a lateral surface of the end plate portion, and perform a orbiting with respect to the fixed scroll; a frame provided at an opposite side of the fixed scroll by interposing the orbiting scroll to support the orbiting scroll; a rotation shaft configured to have an eccentric portion at an end portion thereof, and combined with the orbiting scroll such that the eccentric portion is overlapped with the orbiting wrap in a radial direction; a driving unit configured to drive the rotation shaft; and a rotation prevention member configured to prevent the rotation of the orbiting scroll, wherein the rotation prevention member comprises: a ring portion inserted into a rear surface of the end plate portion of the orbiting scroll; a first key protruded from a lateral surface of the ring portion to be inserted to into the fixed scroll; and a second key protruded from a lateral surface of the ring portion at a predetermined distance from the first key to be inserted into the orbiting scroll.
 7. The scroll compressor of claim 6, wherein the first key is formed to be longer than the second key.
 8. The scroll compressor of claim 7, wherein the first key is formed to be protruded longer than the thickness of an outer circumferential side of the end plate portion of the orbiting scroll.
 9. The scroll compressor of claim 6, wherein the first key is formed to be extended from an outer circumferential surface of the ring portion to the outside thereof and bent in the direction of fixed scroll.
 10. The scroll compressor of claim 6, wherein the second key is formed such that an outer circumferential surface of the ring portion and a surface brought into contact with the orbiting scroll are continuously made.
 11. The scroll compressor of claim 6, wherein a first key groove into which the first key is inserted is formed at the fixed scroll, and the first key groove is continuously formed over an upper end of the side wall portion of the fixed scroll and a support portion supporting the orbiting scroll.
 12. The scroll compressor of claim 11, wherein the first key groove comprises: a vertical portion extended in the upward direction; and a horizontal portion extended in the left/right direction from the vertical portion.
 13. The scroll compressor of claim 6, wherein a second key groove into which the second key is inserted is formed at the orbiting scroll, and the second key groove is formed at an outer circumferential portion of the end plate portion of the orbiting scroll.
 14. The scroll compressor of claim 6, wherein the rotation prevention member is formed to have a yield stress above 300 MPa.
 15. The scroll compressor of claim 14, wherein when the rotation prevention member is formed by sintering stainless steel powder.
 16. The scroll compressor of claim 14, wherein the first compression chamber is formed between two contact points (P1, P2) generated when an inner surface of the fixed wrap and an outer surface of the orbiting wrap are brought into contact with each other, and when an angle having a greater value between angles made by two lines connecting the center (O) of the eccentric portion to the two contact points (P1, P2), respectively, is α, α<360° at least prior to starting discharge.
 17. The scroll compressor of claim 16, wherein when a distance between perpendiculars at the two contact points (P1, P2) is I, I>0.
 18. The scroll compressor of claim 6, wherein a rotation shaft combining portion combined with the eccentric portion at an inner portion thereof is formed at a central portion of the orbiting scroll, and a protrusion portion is formed at an inner circumferential surface of an inner end portion of the fixed wrap, and a concave portion brought into contact with the protrusion portion to form a compression chamber is formed at an outer circumferential surface of the rear surface combining portion. 